The present invention relates to a method for punching a hole in a stack of sheets in an image forming apparatus having a hole puncher.
Recently, use of sorters with an image forming apparatus has become wide spread in the field. Particularly, sorters equipped with a hole puncher.
In a sorter incorporating a hole puncher, sheets are sorted and stored in a plurality of bins provided in the sorter, and the stacked sheets are punched by the punching unit.
Although each bin in the sorter is capable of storing 30 or more sheets, the punching unit sometimes can not punch 30 or more sheets. In conventional methods, the number of sheets which are discharged into each bin is detected, and when the detected number exceeds the number of sheets which can be punched by the hole puncher, the punching operation is skipped. However, when that number is within the number of sheets punchable by the hole puncher, the punching operation is carried out and operation continues. However, sheets vary in thickness, therefore even in the instance the number of sheets is within the punching capability of the hole puncher, the stack can not be punched in same cases. In this case, a motor for driving the punch becomes locked up. When it is detected that the motor is locked up, the motor is reversely rotated returning the punch to the initial position, and then the next operation is performed and the hole left unformed. (Japanese Patent Laying-Open No. 34862/1989).